Carlson6_Angiosperms2 - Angiosperms#2 Bio 1B Fall'07...

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1 Angiosperms #2 Bio 1B Fall ’07 Professor: Thomas Carlson 2 3 ANGIOSPERM LIFE CYCLE (Fig 30.10) Flowering Plant Flower Carpel (megasporophyll) Ovule (megasporangium) Megasporocyte = Mother cell = Diploid precursor cell Megaspore Megagametophyte (7 cells with 8 nuclei) Egg with 2 synergid cells near micropyle Two polar nuclei cell Egg (ovum) Flowering Plant Flower Stamen (microsporophyll) Anther with 4 chambers (4 microsporangia) Microsporocyte = Father cell = Diploid precursor cell Microspore Microgametophyte (2 celled pollen grain with 1 vegetative cell & 1 generative cell) Pollen tube develops from vegetative cell & 2 sperm develop from generative cell Sperm 4 Pollination Carpels divided into three parts (Figs 30.7, 38.2) stigma (top sticky part receives pollen) style (pollen tube grows down through style) ovary (bottom part of carpel which contains ovules that develop into seeds) ovules are located in locule chambers in the ovary placenta : region where ovules attach to ovary wall 5 6
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7 8 Angiosperm Ovule (Figs 30.10, 38.2) structure that contains the gametophyte, and within the gametophyte, an egg (ovum) when it matures, it becomes a seed Eudicot integument forms two outer layers of tissue of ovule that form seed coat (monocots & gymnosperms have one layer of integument) ovules are completely isolated from the outside world by the surrounding sporophytic tissue angiosperm ovules are attached to placenta by a stalk called a funiculus 9 10 11 12
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13 Pollination (Figs 30.10, 30.13, 38.2, 38.4, 38.6) Pollen from anther is deposited on stigma ! germination ! pollen tube (microgametophyte) grows down through style to ovules ! ovules located in locule chambers in the ovary placenta is region where ovules attach to ovary wall 14 15 16 Pollen tube growth (Figs 30.10, 38.2, 38.6) Pollen germinates on stigma Pollen tube grows down through style Pollen generative cell nucleus divides to form two sperm nuclei in pollen tube Pollen tube completes growth to ovule Double fertilization occurs 17 Brassinosteroid hormones support the elongation of pollen tubes 18 Double fertilization in angiosperms (Figs 30.10, 38.6) One sperm nucleus unites with egg to form zygote Other sperm fuses with two polar nuclei to form endosperm (triplopid/3n)
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19 20 Endosperm (tripolid/3n) The triploid cell resulting from the second fertilization goes through a series of mitotic divisions to form endosperm Endosperm contains nutrients e.g., carbohydrates, lipids, and proteins which are be used by the developing embryo 21 Seed Development (Figs 38.2, 38.7, 38.8, 38.9a) Shortly after fertilization highly coordinated growth & development ensues to produce: Embryo: from mitotic division of zygote Endosperm: from mitotic division of triploid nucleus Integuments: outer layer of tissue in ovule which becomes seed coat (eudicots have 2 layered integument, while monocots have 1 layered integument) Carpel: becomes wall of the fruit that encloses the seed 22 23 Seed Comparison: Angiosperm vs Gymnosperm Angiosperm seed: develops from double fertilization Integument: sporophytic (2n)
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